1. Field of the Invention
The invention relates to a sync separator of a video apparatus.
2. Description of the Background
In one prior art sync separator of a television receiver, a black level generator generates from a baseband video signal, a black level restored baseband video signal. In the black level restored video signal, a level that corresponds to a black level is established at a predetermined D.C. level.
The black level restored video signal is coupled to a peak detector that includes a capacitor. In the peak detector, the capacitor is, for example, charged from a switchable source of a first current, during a portion of each horizontal line period, when a difference between a voltage in the capacitor and a voltage representative of the black level restored video signal is at a predetermined polarity. Such difference occurs during a portion of the video line when a sync pulse occurs. The capacitor is discharged by a source of a second current that is smaller than the first current, during the rest of each period. The ratio between the currents is selected such that, in close loop operation, the aforementioned difference occurs when the sync pulse occurs but not outside the occurrence of the sync pulse. The close loop operation maintains the capacitor voltage at a level that is representative of a peak level of the sync pulse.
A signal slicer of the sync separator includes a comparator for generating an output signal in accordance with a difference between the black level restored video signal and a slice level. The slice level is established, in accordance with the peak level of the sync pulse, for example, midway between the peak of the sync pulse and the black level. When the sync pulse occurs in the video signal, the output signal of the signal slicer assumes an active, first logical state; conversely, between consecutively occurring sync pulses, the output signal assumes an inactive, second logical state. It may be desirable to prevent the output signal from assuming the active, first state when, for example, no video signal is present. Video signal may not be present when, for example, a user tunes the receiver to an unused channel.